Java 8: Filter list inside object with another list

Question

I have a list named "foodList" which contains elements of type "Food". The object Food contains a List named "categories" of type "Category".

I am currently implementing a search algorithm to filter food by excluding certain categories.

Excluded Categories are stored inside a List named "excludedCategories".

How can I, using Java 8 and streams, filter the foodList by excluding Food objects whose categoryLists contain any element of the excludedCategories list?

Sample code with loops:

for (Food f: foodList)
{
     for (Category c: f.categories)
     {
          if (excludedCategories.contains(c))
          {
               // REMOVE ITEM FROM foodList
          }
     }
}

Thank you!

Streams are not designed to modify collections. What end result are you looking for? — shmosel
– shmosel, Commented Dec 25, 2019 at 3:48
What would a Category class look like? It seems to me that would best be served by an enum and using an EnumSet instead of a List<Category>. — WJS
– WJS, Commented Dec 25, 2019 at 3:53
A list of food objects containing only food objects whose categories are not inside the excludedCategories List — user2669261
– user2669261, Commented Dec 25, 2019 at 13:34

GBlodgett · Accepted Answer · 2019-12-25 04:06:40Z

5

Streams shouldn't be used to modify the List. Instead you should return a new List with only the appropriate elements in it. You could simply flip the logic a little and use filter:

foodList.stream().flatMap(e -> e.categories.stream())
                 .filter(c -> !excludedCategories.contains(c))
                 .collect(Collectors.toList());

However it would be much simpler to use the built in methods:

foodList.removeIf(e -> !Collections.disjoint(e.categories, excludedCategories));

Collections::disjoint

Collections::removeIf

edited Dec 25, 2019 at 4:06

answered Dec 25, 2019 at 3:53

GBlodgett

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2 Comments

Sunil Dabburi Over a year ago

Your first approach will only contain categories as a list I believe. Not the filtered Food list

WJS Over a year ago

@SunilDabburi You are correct! It will return a List<Category> , not a List<Food>

Sunil Dabburi · Accepted Answer · 2019-12-25 04:31:05Z

1

Use the stream to filter the excluded categories as following

foodList.stream()
        .filter(f -> f.categories.stream().noneMatch(c -> excludedCategories.contains(c)))
        .collect(Collectors.toList());

edited Dec 25, 2019 at 4:31

answered Dec 25, 2019 at 4:10

Sunil Dabburi

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Comments

vivekdubey · Accepted Answer · 2019-12-25 04:42:06Z

0

you can do like this

    foodList.stream().filter(f -> {
        f.setCats(f.getCats().stream().filter(c -> (!excludedCategories.contains(c))).collect(Collectors.toList()));
        return true;
    }).collect(Collectors.toList()).forEach(System.out::println);

answered Dec 25, 2019 at 4:42

vivekdubey

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2 Comments

GBlodgett Over a year ago

What is getCats?

vivekdubey Over a year ago

getCategories is getter method for fecthing category list.

Michael Mesfin · Accepted Answer · 2019-12-26 12:12:26Z

0

foodList.removeIf(f -> f.getCategories().stream().anyMatch(excludeCategories::contains));

you can use removeIf and anyMatch to achieve the desired result

answered Dec 26, 2019 at 12:12

Michael Mesfin

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